1. Field of the Invention
In general, the present invention relates to string trimmers and the rotating heads of string trimmers. More particularly, the present invention relates to the mechanisms contained within string trimmer heads for winding, holding and dispensing new lengths of trimmer line when needed.
2. Prior Art Description
String trimmer machines have been commercially sold for over a quarter of a century. In this period of time, there have been many variations to the design of the string trimmer machine and especially to the trimmer head.
The trimmer head is the part of the string trimmer machine that is rotated by the drive shaft of the trimmer machine. The trimmer head holds lengths of trimmer line that rotate with the trimmer head. The rotating trimmer line contacts and cuts vegetation as it spins.
Depending upon the make, model, and manufacturer of the string trimmer machine, the trimmer head rotates either clockwise or counterclockwise during operation. The trimmer head is affixed to the string trimmer machine by a bolt or nut to the terminus of the drive shaft of the string trimmer including any extension thereto. Threading direction of the bolt or nut is determined by the rotation direction of the drive shaft so that the trimmer head does not unthread from the string trimmer during operation. The mix in the current retail market is roughly evenly split between clockwise and counterclockwise rotating string trimmer machines.
There are many types of trimmer heads on the market. The most common types of traditional trimmer heads are the bump-feed trimmer head and the automatic-feed trimmer head. Both types of trimmer heads contain an internal spool that holds a reserve of wound trimmer line. As the trimmer line wears away, it can be replaced from the internal spool. In a bump-feed trimmer head, short lengths of line are released from the spool when the bottom of the trimmer head is impacted or “bumped” against a hard surface, in an automatic-feed trimmer head, a short length of line is released from the spool without the operator having to manually strike or bump the bottom of the trimmer head on the ground. Many mechanisms exist in the prior art for controlling the release of wound trimmer line from the internal spool of a trimmer head. Bump-activated trimmer heads are exemplified by U.S. Pat. No. 5,881,464 to Collins, entitled Line Head for Flexible Line Trimmer. Automatic-feed trimmer heads are exemplified by U.S. Pat. No. 5,060,384 to Everts, entitled Automatic Head for a Line Trimmer; U.S. Pat. No. 5,109,607 to Everts, entitled Automatic Line Trimmer Head; and U.S. Pat. No. 4,566,189 to Muto, entitled Filament Type Trimmer Apparatus Cutters.
The primary problem associated with such traditional trimmer heads is one of reloading. In order to replenish and reload new trimmer line into the trimmer head, the trimmer head must typically be disassembled and the internal spool removed. This process is often too difficult for many homeowners to complete successfully or even attempt.
Another common problem that often accompanies bump-feed trimmer heads is the problem of line twisting string on the spool. Most bump-feed trimmer heads contain two lengths of trimmer line that extend from opposite side of the trimmer head. Bump-feed trimmer heads rely upon centrifugal forces to pull the trimmer lines from the spool. If the trimmer lines tangle, twist or become buried under subsequent windings or fuse together from heat, the trimmer lines may not dispense in the proper manner. The trimmer head must then be disassembled, the trimmer string unwound and again rewound in the proper manner before the trimmer head will again work as designed. Furthermore, whenever the trimmer string supply is exhausted, the trimmer head must be manually disassembled. The spool is removed and rewound with a new supply of trimmer line. The spool is then reassembled back into the trimmer head. This process is difficult, labor intensive and highly time consuming.
Another problem associated with traditional automatic-feed trimmer heads is the complexity and reliability of the release mechanism that draws trimmer line from the spool when needed. As many homeowners will attest, the mechanism for releasing the trimmer line is usually the first part of a string trimmer machine that falls to work.
Yet another disadvantage of some prior art trimmer heads is that they are designed to rotate in only a single direction, that is, the trimmer head is designed only to be mounted on a clockwise trimmer or on a counterclockwise trimmer but not both. Accordingly, a trimmer head designed for a clockwise trimmer may not work on a counterclockwise trimmer. Furthermore, some parts from a clockwise trimmer head cannot be interchanged with any of the parts from a counterclockwise trimmer head. This requires a trimmer head manufacturer to create two sets of manufacturing tools, one for clockwise trimmer heads and one for counterclockwise trimmer heads. This significantly increases the cost associated with manufacturing trimmer heads. Furthermore, it results in each trimmer head design having two different models, one for clockwise rotation, and one for counterclockwise rotation.
A need therefore exists for a string trimmer head that has an inexpensive yet reliable mechanism for dispensing trimmer line when needed. A need also exists for a string trimmer head that dispenses trimmer line with less likelihood that the trimmer line will tangle, twist, or bind. Furthermore, a need exists for a trimmer head that does not have to be disassembled to have new string added. Lastly, a need exists for a trimmer head that can be manufactured inexpensively with few operating parts and can operate either as a uni-directional of bi-directional trimmer head on trimmer machines. These needs are met by the present invention as described and claimed below.